包中的全局变量-更推荐使用哪种方法? [英] Global variable in a package - which approach is more recommended?

问题描述

我确实知道一般来说全局变量是邪恶的，我应该避免使用它们，但是如果我的程序包确实需要一个全局变量，那么这两种方法中哪个更好?还有其他建议的方法吗?

I do understand that generally global variables are evil and I should avoid them, but if my package does need to have a global variable, which of these two approaches are better? And are there any other recommended approaches?

1. 使用程序包可见的环境

1. Using an environment visible to the package

pkgEnv <- new.env()  
pkgEnv$sessionId <- "xyz123"

使用options

options("pkgEnv.sessionId" = "xyz123")

我知道还有其他一些线程在询问如何实现全局变量，但是我还没有看到关于推荐哪个变量的讨论

I know there are some other threads that ask about how to achieve global variables, but I haven't seen a discussion on which one is recommended

推荐答案

某些包使用隐藏变量(以.开头的变量)，例如.Random.seed和.Last.value在基R中执行.可以做到

Some packages use hidden variables (variables that begin with a .), like .Random.seed and .Last.value do in base R. In your package you could do

e <- new.env()
assign(".sessionId", "xyz123", envir = e)
ls(e)
# character(0)
ls(e, all = TRUE)
# [1] ".sessionId"

但是在您的包裹中，您无需分配e.您可以使用.onLoad()挂钩在加载程序包时分配变量.

But in your package you don't need to assign e. You can use a .onLoad() hook to assign the variable upon loading the package.

.onLoad <- function(libname, pkgname) {
    assign(".sessionId", "xyz123", envir = parent.env(environment()))
}

请参见此问题及其答案，以获取有关软件包变量的一些很好的解释

See this question and its answers for some good explanation on package variables.

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